This invention relates to a recording and/or reproducing apparatus for compressed data obtained on bit compression of digital audio signals. More particularly, it relates to a recording and/or reproducing apparatus in which at least a signal reproducing system and a signal recording system are provided separately from each other.
In e.g. JP Patent Applications Nos. 2-221364, 2-221365, 2 -222821 and 2-222823, the present Assignee has proposed a technique of bit compressing input digital audio signals and recording them in a burst fashion based on a predetermined volume of data as a recording unit.
With this technique, AD (adaptive differential) PCM audio data prescribed in an audio data format of CD-ROM XA or CD-I (CD-Interactive) are recorded on or reproduced from a magneto-optical disc used as a recording medium in a burst fashion. Recording is made in this case with e.g. 32 sectors of the ADPCM data and several linking sectors as a recording unit for interleaving. Table 1 shows ADPCM audio levels in CD-I format or CD-ROM XA format in conjunction with standard CD (compact disc) format (CD-DA format).
TABLE 1 sampling number of bits dynamic CD- frequency for quantization range bandwidth playback time ROM level (kHz) (bit) (db) (kHz) stereo monaural CD-I XA PCM CDDA 44.1 16 98 20 1 -- .smallcircle. .smallcircle. AD A 37.8 8 90 17 2 4 .smallcircle. -- PCM B 37.8 4 90 17 4 8 .smallcircle. .smallcircle. C 19.8 4 90 8.5 8 16 .smallcircle. .smallcircle.
Referring to Table 1, in e.g. the level 8 mode, digital audio data are compressed to approximately 1/4, such that the playback time of a disc recorded with the level B mode is four times that with a standard CD-DA format. This means that, since the recording/playback time about equal to that of a standard disc with a diameter of 12 cm may be achieved with a smaller size disc, the size of the recording and/or reproducing apparatus may be correspondingly reduced.
However, with the level B mode, for example, the four channel ADPCM data are presented cyclically at an interval of four sectors as the inherent recording data conforming to the CD-I format, so that, when a single channel is reproduced, it becomes necessary to take out one sector data out of four sector data periodically. However, it is practically impossible to effect recording of a channel of ADPCM data because of the problem of interleaving extending to adjoining channels. For this reason, with the above mentioned prior-art technology, continuous ADPCM audio data are time compressed at intervals of, for example, 32 sectors, and linking sectors are appended before and after the sector in order to take account of the interleaving extending to data of the adjoining sectors to effect sector-continuous recording in a burst fashion.
Meanwhile, a recording and/or reproducing apparatus, provided with two-channel recording and/or reproducing units, such as a so-called double-cassette tape recorder, has been offered to the market. It is highly probable that the demand will be raised for a recording and/or reproducing apparatus for compressed data which is provided with such two-channel recording and/or reproducing units. If these units were provided separately, production costs would be doubled. On the other hand, it is highly desirable that a so-called dubbing function be accorded to such apparatus provided with the two-channel recording and/or reproducing units so that a predetermined recording medium is reproduced by a reproducing system of one of the units for recording by a recording system of the remaining unit. If such dubbing function is to be implemented by the above mentioned recording and/or reproducing apparatus for compressed data, the same time that is necessary for usual playback is required for dubbing. Thus a function for dubbing at a higher speed is desired.